Background Methylenetetrahydrofolate reductase (MTHFR) synthesizes 5-methyltetrahydrofolate, the major carbon donor in remethylation of homocysteine to methionine. A common MTHFR mutation, an alanine-to-valine substitution, renders the enzyme thermolabile and may cause elevated plasma levels of the amino acid homocysteine.

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OBJECTIVE:To prospectively examine the relation between television watching and body fat change in children from preschool to early adolescence. METHODS: In a longitudinal study, 106 children were enrolled during preschool years (mean age 4.0 y) and followed into early adolescence (mean age 11.1 y). Parents completed an annual questionnaire on the child's television and video habits. Body mass index (BMI), triceps skinfolds, and sum of five skinfolds were recorded yearly at annual clinic visits. Longitudinal statistical analyses were carried out using mixed modeling procedures to control for potential confounding by a number of factors. RESULTS: Television watching was an independent predictor of the change in the child's BMI, triceps, and sum of five skinfolds throughout childhood. Its effect was only slightly attenuated by controlling for the baseline body fat, level of physical activity (as measured repeatedly by Caltrac accelerometer), percent of calories from fat, total calorie intake, or the parents' BMI or education. By age 11, children who watched 3.0 h or more of television per day had a mean sum of skinfolds of 106.2 mm, compared with a mean sum of skinfolds of 76.5 mm for those who watched less than 1.75 h per day (P ¼ 0.007). Furthermore, the adverse effect of television viewing was worse for those children who were also sedentary or had a higher-fat diet. CONCLUSIONS: Children who watched the most television during childhood had the greatest increase in body fat over time. Healthy lifestyle education designed to prevent obesity and its consequences should target television-watching habits of children.

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